The earth is inhabited by monsters. They crave every opportunity to break through and populate neighboring planets. It is impossible to predict all the tricks that they are willing to perform for this. It remains to methodically deal with attempts to penetrate, leaving them as few chances as possible. Ideally, none, but the ideal, as we know, is unattainable.
The article on planetary protection - protecting other worlds from unauthorized colonization by earthly microbes - just wants to start with something like that, and this is the case when such a desire is appropriate. We know that not only the colonialists themselves, but also the diseases they brought, played a significant role in the fate of the indigenous peoples. Something like this can happen in space. Even the minimal option, in which the local environment is simply populated with earthly life, which does not interact with anyone and does not particularly bother anyone, is extremely unpleasant. It does not allow scientists to explore the heavenly body in its original form, as it was before our arrival. Therefore, efforts aimed at preventing such a prospect seem logical.
This picture also has a downside. Remember Neil Armstrong and his colleagues? The famous earthling who went down in history thanks to his first step on the lunar surface? Before that there were years of training and flying, but they are usually not remembered, only the first step. And what did the grateful earthlings do with the astronauts? They put all three in a sealed chamber mounted on a camper van, and upon arrival in Houston, together with the attendants, they were sent to a strict three-week quarantine - in a sealed room with the ability to communicate with the press through a glass partition.
The lunar soil samples collected by the astronauts were even more thoroughly tested with tests on laboratory mice and plants. Of course, by 1969 no one believed in the selenites inhabiting the moon, but the possibility of the presence of microorganisms there was taken seriously, even if it was considered as unlikely.
The boundaries of life
In the XX century, the Moon began to be habitually perceived as a celestial body, completely devoid of life. Meanwhile, although such a view is plausible, it is not at all necessary. The fact is that we know our celestial neighbor, albeit relatively well, but literally superficially - a few centimeters deep. Everything below is more or less predicted by calculations, and nothing more. According to them, it turns out that already at a depth of several meters, the temperature is quite positive, its fluctuations are small, and there is almost no cosmic radiation. It remains to find out how there is business with water. According to the latest data, it looks like it is on the Moon, at least in places. In short, everything an honest microbe needs to live and feel good.
Similar microbes - capable of thriving underground at great depths and in complete isolation from the rest of the biosphere - exist on Earth. In 2002, in one of the mines in South Africa, they found the bacterium Desulforudis audaxviator, living in isolation at a depth of 2-3 km in a highly alkaline solution at a temperature of about 60 degrees and completely without oxygen. The latter is a strong poison for desulforudis, and this makes one think that the bacteria left the earth's surface long ago. They have everything else. They know how to use sulfur, nitrogen and molecular hydrogen in their metabolism, absorb ready-made organic matter, if one appears nearby, extract carbon from carbon dioxide and carbon monoxide, as well as formates (salts and esters of formic acid), independently synthesize all 20 amino acids, swim in the search for a better life with the help of flagella and "pupate" in disputes if the search fails. Craftsmen for all flagella! If our planet becomes something like the Moon, then desulfurdis from their depths simply will not notice it.
Approximately the same can be said now about any seemingly lifeless body of the solar system.We know them from afar, at best - thanks to a probe flying thousands of kilometers, and more often - through a telescope.
On Mars, conditions are simpler. There is an atmosphere, albeit very rarefied, there is definitely water there. It is not clear how much of it and how often it occurs in the form of a liquid, but the very fact of the presence of water is beyond doubt. It is also not surprising that the number of terrestrial microorganisms known to science, capable of living and even multiplying on the Red Planet, is measured at least by numbers greater than one. Such experiments have been carried out several times over the past couple of decades. Back in 2005, the ability to live in conditions resembling those of Mars was demonstrated in blue-green algae of the genus Chroococcidiopsis. You just need to protect them from ultraviolet radiation - a layer of soil only a millimeter thick is suitable for the role of a barrier. Subsequent work made it possible to expand the list of potential "survivalists" to include a number of other organisms, mainly extremophiles, whose terrestrial habitat may seem surprising to us.
Let us clarify that, as far as one can judge, there is no life on the surface of Mars, and this is not surprising. The planet has a very rarefied atmosphere and has almost no magnetic field at all. Collectively, this means that the radiation background on the surface is almost the same as in space. And what Mars has there deeper, we do not know yet.
In the last decade, experiments with the survival of various terrestrial organisms in outer space have become commonplace, since it is not far from us. Staying there is safely tolerated by bacteria, fungi, algae and even tardigrades - small multicellular animals about a millimeter in size, close relatives of arthropods. A series of three (so far) EXPOSE experiments: -E, -R and -R2, in which containers with experimental (bacteria, fungi, plant seeds, etc.) in a special installation were set for aboard the ISS, into open space, either without any special protection, or with shielding, which made it possible to make the radiation environment similar to the Martian one. The exposure period ranged from nine months to three years. Some of the test subjects survived.
Today, the number of species of terrestrial organisms that can withstand the effects of outer space and come to life, later in a more suitable environment, is about a hundred. Most likely, in fact, there are significantly more of them, since viable microorganisms were found on the outer surfaces of the ISS. They got there on their own, without the help of experimenters.
Statement of a question
The possibility of bringing life to other celestial bodies was recognized as a problem quite a long time ago, on the threshold of the space era. For the first time, the thought sounded at the congress of the International Astronautical Federation in 1956. In 1959, control over planetary defense was transferred to the Committee on Space Research, or COSPAR.
In January 1967, the then space powers signed the "Treaty on the Principles Governing the Activities of States in the Exploration and Use of Outer Space, Including the Moon and Other Celestial Bodies," adopted by a resolution of the UN General Assembly a month earlier. Its Article IX is directly related to the topic of our conversation today, establishing that the participating States strive to conduct research and study of cosmic bodies in such a way as not to pollute them as much as possible. This rule is still in force. It is very likely that in the coming years it will have to be changed or edited, since from our time one can already see the outlines of the future that will arise when humanity moves from "study and research" to other forms of behavior in relation to other planets.
All space missions, depending on the danger of contamination of their targets by terrestrial microbes, are divided by COSPAR into four categories: from flyby to descent vehicles sent to where life is suspected. A separate category, fifth, is assigned to vehicles that are fully or partially returned to Earth. It is logically divided into two subcategories: return from where life is clearly absent, and from where it is possible.
It should be noted that at the level of the basic concept, planetary protection is perceived as a temporary measure - until the beginning of colonization or, at least, regular manned missions. After that, keeping the situation under control will be much more difficult, if not impossible.
As Sagan said
I apologize to people who do not like mathematics, but you can't do without it at all. To determine the admissibility of a particular space mission, the probability of bringing earth life there is used. The probability should be small enough. To estimate it, the Coleman – Sagan formula, proposed in the 1960s, is still used, in which the initial (at the time of launch) the number of microorganisms on the spacecraft is multiplied by seven modifiers, which represent the probabilities that the “passengers” will survive the corresponding stage of the mission.
The result of the multiplication is the final contamination probability, which must be less than 10-4.
Most of the values involved in the procedure are known to us very approximately. It is almost impossible to say, for example, what the likelihood is of how quickly a probe sent to Europa will end up in the ocean under an ice sheet. Meanwhile, this or that assessment changes the picture drastically. Or the descent vehicle will find itself relatively quickly in liquid water - then the probability that the bacteria that have survived to this moment will "wake up" is equal to unity. Or the probe for a geologically significant time will remain for "sterilization" in a vacuum and under the influence of powerful radiation - and then nothing alive will definitely remain on it.
Nevertheless, the criterion for the admissibility of a particular mission according to Coleman and Sagan should be a computation result less than 10-4… Why such a figure was chosen, it is not clear what is another reason for both criticism of the formula and proposals for alternative solutions. One of these appeared several years ago in a report on planetary protection measures in the study of the icy celestial bodies of the solar system. First of all, of course, Europe is meant, but it is not alone - the problem is inherent in other cosmic bodies as well.
Alternatively, experts offer a list of questions about the available data for a particular celestial body:
Is there any reason to believe that there are no:
- the key chemical elements for earthly life?
- physical conditions suitable for life?
- available sources of chemical energy?
Is there any reason to deny that the probability of a ship's contact with any habitable environment in the next thousand years exceeds 10-4?
Is there evidence that the lack of nutrients in the aquatic environments of icy moons will prevent the survival of irradiated and dried microbes?
Is there any confidence that a five-hour exposure of the device at 60 degrees Celsius (that is, with an easy disinfection option) will eliminate all types of microbes that can spread on the target body?
An affirmative answer to any of these questions leads to a simplified assembly of the apparatus, and only a firm "no" in all seven cases means that exclusive precautions must be taken. Now we cannot say with certainty that this approach will prevail in this edition, but so far it looks clearer than the traditional one.
Visit on your own
There is one more complication that needs to be taken into account. This is the ability to spread live microorganisms in a natural way.Almost all the planets of the solar system, except for the largest, are sources of meteorites, which are formed when other meteorites hit them - larger ones. With the Earth, this happens, apparently, relatively rarely. Gravity and a fairly dense atmosphere limit the possibility of knocking out any noticeable masses of matter from the planet by events of a frankly catastrophic nature, such as the one that led to the extinction of the dinosaurs. Nevertheless, it is likely that future explorers of Mars will stumble somewhere on a piece of their home planet, which has overcome the depths of space without any human participation.
On Earth, meteorites of Martian origin are found from time to time. Their origin is determined by the isotopic composition of gases in micropores, since the corresponding parameters of the Martian atmosphere are now known exactly. At the moment, there are more than two dozen Martian meteorites at the disposal of scientists, and their number is gradually increasing. According to rough estimates, about half a ton of matter, once part of a neighboring planet, falls to the Earth annually.
One of the meteorites, found in 1984 in Antarctica (its open spaces are a popular place for searching for meteorites, since it is especially easy to look for them there: a stone lying in the snow must have fallen from the sky), became famous precisely for the fact that, during microscopic examination, fossils were found in its thickness, surprisingly reminiscent of bacteria known to us, only smaller. This find not only breathed new life into the debate about the existence of life on Mars, but also gave skeptics a new argument against the concept of planetary protection as such. Indeed, why waste money if everything has already arrived by itself?
This point of view has not yet triumphed, since the time factor plays against it. A human probe flies to its target for several years, in rare cases - a decade. Before falling to Earth, the famous meteorite was in space for about 15 million years, during which time nothing living could remain on it, only fossils (and their origin is also controversial). Perhaps some other rock will arrive faster, but the likelihood that it will fall into such a successful orbit that will allow it to compete in speed with the probe is vanishingly small.
In a clean room
The practical actions of NASA and ESA look quite simple, and traces of the equations in them are not visible to the naked eye. All equipment sent into space is assembled in a clean room - a special room with a strictly controlled composition of the atmosphere. Ventilation supplies air through sophisticated cleaning systems, maintaining a slight excess of pressure in the room in relation to the outside world. This is done so that even with leaking joints, air flows from the assembly room to the outside, and not vice versa. Air supply systems are designed and located so as not to create turbulent eddies anywhere. Uniform laminar flows only. If suddenly a speck of dust gets inside, then let it lie in place, and not spin in an air stream.
Of course, the clean room is often cleaned and the staff walk through it in overalls that resemble spacesuits, and, in fact, differ little from them.
In serious cases, such as a flight to Mars, heat-treatable components are kept for thirty-five hours at temperatures above one hundred and eleven degrees Celsius. More delicate parts are treated with alcohol, hydrogen peroxide or radiation. Something that cannot stand disinfection at all, like an on-board computer, is sealed as tightly as possible during assembly.
Taken together, the precautionary measures should ensure that the total number of microorganisms is reduced to 300 thousand for the entire spacecraft. This is how both Vikings were treated in the 1970s, disinfection of which is still considered the standard.
300 thousand - Is it a lot or a little? On the one hand, very few.For comparison, one gram of soil contains, depending on the climatic zone, from several million to several billion bacteria. On the other hand, in order to reproduce, once in favorable conditions, a single one is enough.
Moreover, even a sophisticated struggle for purity means that the struggle is real, not purity. A decade ago, microbiologists studied three clean rooms at the Jet Propulsion Laboratory and NASA. Found more than 100 species of bacteria, almost half of which were previously unknown to science. Among the finds are mainly oligotrophic (that is, accustomed to scarce food) species that are rare in ordinary places, which, having fallen into the harsh conditions of carefully guarded sterility, felt freedom from competitors. It is they, who are accustomed to the unattractiveness of being, who are considered the most likely "uninvited guests" on Mars, and elsewhere. Repeated measurements in 2013 showed about the same. However, even bad defense is better than none.
Instead of a conclusion
The reader probably noticed that by "life" we mean something very similar to earthly life, with proteins, amino acids, DNA and other details so familiar to us. Only it makes sense to protect it from the earthly. Any significant difference in design will make the two environments immiscible and likely save them (and us) most of the trouble.
Nevertheless, today we only know earthly life and are trying to plot a graph by one point, and this is difficult.